Synchronizing device



0. C. TRAVER SYNGHRONIZING DEVICE Nov. 24, 1925- 2 Sheets-8heet Filed July 29 1922.

T igl.

lm/en-kor: Oliver C. Tran/er;

l lis XI-E-Eofh e Nov. 24, 1925 1,563,120

' v o. c. TRAVER SYNCHRONIZING DEVICE g 2' Flled July 29, 1922 2 shfgtliskfi et 2 l'nVeh -l: or: O I New C. Traver;

b5 I l-hs him-neg and its scope Patented Nov. 24, 1925.

UNITED STATES PATENT OFFICE.

OLIVER C. TRAVER, 0F SCHENECTADY, NEW YORK; .AgSIGNOR TO GENERAL ELEC- TRIO Columnist, A CORPORATION SYNCHRONIZ Application filed My 29,

To r ZZ whom it may concern: I Be it known that I, OLIVER'C. TRAYER, a citizen of the United States, residing in- Schenectady, in the county of Schenectady, State of New York, have invented certain new and useful lmprovements in Synchronizing Devices, of which the following is a specification.

My invention relates to improvements in synchronizing devices and has for an object to provide an improved synchronizing device for automatically controlling the operation of connecting an alternating current dynamo electric machinelto an, alternating current electric circuit whereby the connec tion can be made substantially 'onlyat the instant when the electromotive forces ofthe machine and circ'uit are alike in frequency, phase and value. My invention will be better understood from. the-followingdescription taken in connection with the accompanying drawing,

will be pointed out in the appended claims- Y Figure 1 illustrates diagrammatically an embodiment of my invention, and F igs.-2' to 11, inclusive, are vector diagrams illustrating the principles upon which myinvention is based. i v; t

For purposes of illustration, I haveshown in Fig. 1 an embodiment of my invention as applied to a three phase alternating current electric system. comprising an alternating currentielectric circuit such as a bus 1 to which maybe connected one. or more dyna-, mo electric machines 2 or sources of alters natin'g current in parallel as is well known to the art. I, have illustrated the dynamo electric machine 2'as an alternatoradapted i to be connected to the busi by any suitable circuit controlling means 3 arranged to con trol a eircuit 4 between the bus land the alternator The circuit controlling means 3 preferably comprisesan electrorcsponsive closing means such as a closing coil 5 connected" in a control circuit 6' whichmay be connected across a-eontrol bus'7, -and which mavinclude an auxiliary ,switchS arran 'ed to be controlled by't-he. circuit,contmllmg' controlling means, is open and open when the circuit controlling means is closed. For. controlling the control circuit 6, I provide electroresponsive means comprising OFNEW YORK.

ING DEVICE 1922. Serial No. 578,475.

a plurality of circuit. controlling members Rese 9,10 and I1whi'ch are arranged to control contacts 12, '13 and 14or 15, respectively, arranged in series in the control circuitfi. The electroresponsive ans may comprise a plurality of differentially acting electroresponsive devices or relhys 16, 17 and 18 which may be of the shaded pole induction disk motor type, each element comprising an induction disk anda. plurality of motor ele-' ments arranged to exert opposing torques thereon.

For energizing the motor elements of the relays I provide, in accordance with my invention, a plurality of sources of electromotive force such as potential transformers- 19, 20 and 21, 22 connected in circuit with the bus 1 and'the alternator 2, respectively, on opposite sides of the circuit controlling means 3. The [secondaries of the transformers 19 and 21 areconnected in circuit for opposing electromotive forces when their'electromotive forces are in phase and I I the. secondaries of the transformers 20" and 22fare connected in circuit for cumulative elect-romotive forces when their electromotive'forces are in phase.

The relay 16 which controls circuit con- 'trolling member 9 may comprise an induction disk 23,. shaded pole motor elements 24 and 25 arranged to exert opposing torques thereon, and suitable means suchas a drag magnet 26 for exerting'a.'reta-1'ding force on the disk 23 so as to obtain a time delay action in the movement the-reofil Movementof the disk- 23in a direction to carry circuit controlling member 9 away from circuit closing position is limited by any suitable means such as a stop 26', The position of'the stop 26' relatively to the contaets 12 may be determined in! accordance with the angular movement of the disk 23' necessary to providethe time delay desired and, in a practical embodiment of my-inven tion I have arranged .the stop 26 and the contacts 12- so that the disk 23 may have an angular movement of approximately {180 Motor element24 is provided with an energizing Winding 27 connected in series rela,.

tion with the secondaries of the potential transformers 19 and '21 and motor, element 25 isprovidedwith an energizing winding 28 connected ii series relation with the seeondaries of the potential transformers 2Q and 22. The motor elements 24 and 25 tend to exert opposing torques on the disk 23 irrespective of the directions of current flow in their windings 27 and 28, respectively.

The relay 17 which controls circuit con trolling member 10 may comprise'an induction disk 29 and shaded pole motor elements 30 and 31 arranged to exert opposing torques thereon. Motor element 30 is provided with an energizing winding 32 connected in series relation with the secondaries of the transformers 19 and 21, and motor element 31 is provided with'an energizing winding 33 connected in series relation with the secondaries of the transformers 20 and 22. The motor elements 30 and '31 tend to exert opposing torques on the disk 29 irrespective of the directions of current-flow in their windings 32 and 33 respectively. The disk 29 isso shaped andythe shaded poles of themotor elements 30 and 31 so arranged with respect to thedisk 29vthat in the event of either of the motor elements30, 31 predominating to turn the disk'29,'the torque exerted by the stronger element is increased while the torque exerted by the weaker ele; ment is decreased. One way to obtain this "effect is to remove a segment of the disk 29 and arrange theshaded, poles as-shownso that an increasing'area of the disk is pre-. sented adjacent the shaded pole faces of themotor element tending to exert the greater torque and a decreasingjarea of the diskadjacent the shaded pole faces of the motor element tending to exert the smaller torque. This construction and arrangement of parts" also provides for a quick positive movement of the disk 29substant1ally of the nature or a snap action which is desirable. Movement of the disk 29 in a direction to carry circuit controlling member 10 away from circuit closing position is limited by any suitable means such asa stop 34; I

, The relay 18 which controls circuit controlling member 11 may comprise an induction disk 35 and shaded pole motor elements 36 and 37 arranged to exert'opposing torques thereon. The motor element 36 is provided with an energizing winding 38 connected across the terminals of the secondary of transformer 21 and the motor element- 37 is provided with an energizing winding 39 connected across the terminals of the secondary of the transformer 19. The motor elements 36 and 37 tendto exert opposing torques on the disk 35 irrespective of the directions of current flow in their windings 38 and 39 respectively. Obviously-when the motor elements 36 and 37 exert equal torques, that is to say, when the voltage of the alternator 2 is substantially equal to the voltage on the busl, the disk 35 will tend to remain stationary and the contacts 14 and 15 closed, but upon the occurrence of a predetermined difierence in these voltages,- the disk 35 will 'ment 18 or other equivalent means.

be turned in one direction or theother to open ,either contacts 14 or 15. One of the contacts of each of the pairs of contacts 14 and 15'may be provided witha depending or tail portion 40 extending into the path of movement of the circuit controlling membeiull and each of these-contact members may also be resiliently mounted for the purpose of maintaining itself in engagement with its cooperating contact. The contacts with the depending portions 40 also act to limit the movement of the disk 35 in either direction and tend to return the disk 35 to an intermediate position when the torques exerted by the motor elements 36 and 37 are substantially equal.

For the operation of my synchronizing device, it will be desirable to refer to Figs. 2 to 11, inclusive, which are vector diagrams illustrating the principles upon which my invention is based. In these diagrams, the heavy solid lines designated E and shown in a fixed position as a reference line, represent the voltage on'the bus 1 or a voltage proportional thereto as, for example, the voltage across the secondary of each of the transformers 19 and 20. The heavy solid lines designated e represent the voltage of the alternator 2 ,or a voltage proportional thereto as, for example, the voltage across the secondary of each of the transformers 21 and 22. The vector e is assumed to rotate in accordance with the phase relation of the tWo-electromotive. forces to be synchronized. The heavy dashed lines designated e, represent the voltage 6 reversed. The vectors E, e and e, are assumed equal in lengthas this-is a condition for controlling-the control circuit 6 under the control of relay e light solid lines designated m and y. repre sent the vectorial differences of E and a, and E and 6, respectively, that is to say, as ,represents the vectorial difference and y the vectorial sum of E and e. The voltages m and 3/, in accordance with their relative values: control 'the o eration of the relay elements 16 and 17. .or convenience, the. vector dia.-'

gramsare assiuned 'to'be divided'into four quadrants a, b, c, and cl respectively as indicated in Fig. 10. v

Fig. 2 represents the in-phaseicondition of the voltages on the bus 1 and the alternator 2. In this case, the vectors E and 'e coincide, w is zero and 9!, has its maximum value.

Fig. 3're resents the voltage of-the alternator less t an 90 degreesout of phase with the voltage on the bus'l, that is-to say voltage in quadrant a. In this case, voltage y is greater than voltage "a2.

Fig. 4- represents the voltage of the alternator 2, 90 degrees out of phase with the voltage on the bust; Tn thiscase, voltage m equals voltage 3 voltage on the bus 1. 1(1

Fig. 5 represents the voltage of the alternator 2 more than 90 degrees and less than 180 degrees out of phase withthe' Voltage on thebus 1, that is to say, voltage 0 in quadrant 7). In-this case voltage y is less than voltage 00.

Fig. 6 represents the voltage of the alternator 2, 180 degrees out of phase with the In this case ac has attained its maximum value and g is zero.

Fig. 7 represents the voltage of the alternator 2 more than 180 degrees and less than 270 degrees out of phase with the voltage on the bus 1, that is to say, voltage 6 in quadrant c. In this case voltage a is greater than voltage y.

Fig. represents the voltage of the alternator 2, 270 degrees out of phase with the voltage on the bus 1. In this case, voltage .7: equals voltage y.

Fig. 9 represents the voltage of the alternator 2, more than 270 degrees and less than 360 degrees out of phase with the voltage on the bus 1, that is to say,'voltage e in quadrant (Z approaching phase, coincidence with voltage E. In this case voltage 3 is greater than voltage at.

Fig. 10 is a summary indicating the relative values of the voltages :r and y in the different quadrants and under the different conditions heretofore considered.

From these figures, particularly Fig. 10, and assuming disk not retarded in its movement and disk 29 circular and motor elements 2-1 and 25 and also 30 and 31 to be so alike in features of construction that, when their respective windings 27 and 28 and also 32 and 33 are equally energized, equal torques are produced, .it will be observed that through a certain range of phase difference, viz, 90 degrees to 270 degrees or when voltage 3 is less than voltage :12, as in quadrants b and 0, motor elements 24 and 30 would predominate to turntheir respective disks counter clockwise, that is, the disk 23 to circuit opening position and the disk 29 to circuit closing position and that through another certain range of phase diflerence, viz, 276 degrees to 90 degreesor when voltage y is greater than voltage m, as in quadrants d and a, motor elements 25 and 31 would predominate to turn their disks 23 and 29 clockwise, that is, disk 23 to circuit closing position and disk 29 to circuit opening position; Under'these condition; the disks 23 and'29 would not simuL taneously be in circuit closing position.

In order that the circuit controlling means 3 may be closed onlywhenthe electromotive forces of the bus 1 and alternator 2 are substantially alike in phase, frequency and value. I so constructand arrange the relays 16, 17 and 18 that the movable elements thereof must simultaneously be in predetermined positions. For this purpose, I may closed when the difference in voltages of the alternator 2 and bus 1 is within a predetcrmined amount which in a practical embodiment of my invention, I have taken so that the voltages must be within tive per cent of each other.

Referring nowto Figs. 1 and 11, motor element 25 may be so constructed as to predominate over motor element 21 to start disk 23 moving to circuit closing position when voltage 0 has reached a position 6, prior to phase coincidence where. voltage 3/ has a value 7 and voltage 50 the corresponding value a", and contacts 12 will be closed with a time delay, and when voltage 6 passes through phase coincidence to a position 0 where .crand y again have substantially the same values in, and y,,'motor element 2-1 will predominate and move disk 23 to circuit openlng position. In a practical embodi- -ment of my invention voltages in, and 3 have substantially the values -10 and 220 volts respectively. Thus, as voltage e moves to and away from phase coincidence through the range of phase difference from a, to '6 disk 23 will be moved toward circuit closing position with a time delay, while in the range of phase difference from through phase opposition to 6,, disk 23 will be moved toward circuit opening position. For the values of the voltages at and 3 and the action herein set forth, it will be obvious that motor element 24 should be constructed to exert the predominanttorque when voltage 00 is greater than 40 volts and voltage 3 less than 220 volts. In which case motor element 25 will exert the'predomiuant torque when voltage as is less than 40 volts and voltage greater than220 vol t s.

The position 6, of the voltage 0, Fig. 11 corresponds to thep arts in position as shown in Fig. 1. In this position, more of the disk 29 is adjacent the pole faces of motor element 30 than is adjacent the pole faces of motor element 31. Motor element 30 then redominates to hold disk 29 in circuit closmg position. As voltage (1 moves to sub- 1 stantially phase coincidence, that is, ,posi-' tion a voltage :1: decreases to m, and voltage 3 increases to 3 and motor element 31 then predominates to move disk 29 quickly to circuit opening position. According to my 111- vention, the particular position of e, is preterably, for practical purposes, just before phase coincidence as this allows somewhat for the time necessary to close the circuit controlling means 3. In a practical embod The motor 70 29 will be presented ment of m invention, motor element 31 is constructe 'to predominate when voltages a: and y reach substantially the values and 220 volts respectively. When motor ele- "ment 31 predominates to move the disk 29 clockwise, an 'increasin area of the :disk ad acent its pole faces and a decreasing area adjacent the ole faces element of motor element 30. Consequent y, motor element 31 will be rendered more effective in its predominance and the efiect of motor decreased. The-disk 29will therefore be quickly moved to circuitfopening tion, the voltage 6 must reach osition and more of the disk 29 willbe adacent the ole faces of motor element '31 and less a ja'cent the pole faces of motor element 30. Consequently voltage as will have to increase a preciably and voltage 3 7 decrease according y in order that motor element 30 may predominate to move the disk 29 to circuit closing position. In order toinsure thatthe disk 29 may not move to circuitclos'ing position until after the disk 23 has moved to circuit opening position, I construct the motor elements 30 andv 31 so that I with the disk 29 in circuit opening posia position e, such as, for example, substantially uadrature or degrees from phase c'oinci ones where volta es m and 3 are substantially equal, (see ig. 4) before motor element 30 can predominateto move the disk 29 to cir cuit closing position. The particular 'posi tion of e, is immaterial, the main requisite being that the position of e where motor element 3O predominates to move disk 29 to circuit closing position should be in phase.

displacement subsequent tothe position e, where motor element 2i predom nates move the disk. 23-te circuit opening posh tion. In a practical embodiment of my invention, the values of the voltages a2 and y,

corresponding to the positions, of the voltage 6, are each substantially 150 volts When motor element 30 predominates to move the disk 29 to circuit closin position, the disk (see Fig. 1) will remain substantially in this position until voltage 2 reaches the .posi 'tion e when motor element 31 will again predominate and move the disk 29 to circuit opening position as heretofore set forth.

' Thus, as voltage 6 moves to'a-nd away from phase coincidence through the tan e of v hase difierence'from e, to e the disk 29 willbe in circuit opening position while in the range of phase difference from a, throu h hase oppos1tion to- 6,, the disk 29 wiil in circuit *cldsingposition.

It will therefore be obvious that the difference between the frequenciesof the alternator and bus voltages must "beless than a 'predeterminedamount in orderthat the, disk" 23 may have tnne'to move to circuitfclosing v 1 position before disk 29 is moved to circuit opening position, Moreover, the range of;

during a; limited number of de phase difierence over which both the disks 23 and 29 may-simultane'ouslybe in circuit closing positionis limited and consequently the control circuit 6 can be completed only synchronlsm and not after. his allows somewhat'for the time required to close the circuit controlling means 3. It is, of course, a'ssumedthat the voltages ofithe alternator 2 and bus 1 are equal so that contacts 14 and 15 remain closed. If these voltages are not equal one or the other of the contacts 14 and 15; will be opened in consequence of the differential action of the motor elements 36, 37 on the disk 35 and therefore'the control circuit 6 will-be held open even though thealternator voltage has the same frequency as, and is in phase with, the bus voltage. It 1s therefore clear that the control circuit .6

controlling the operation of closing the circuit controlling means 3 can be closed only when the voltages of the alternator 2 and thebus' 1 aresubstantially alike in phase,

frequen'cy, and value. It is moreover clear thereof, as shown and describe ,but may use such modifications, substitutions or equivalents thereof, as are embraced within the spirit of my invention; 4

What I cla m as newand desire to se cure by Letters Patent of the United States 1s:

1. a system 'of the class described wherein two sources of alternating electromotive force are to be synchronized, a, switch for connecting the sources, and means for controllingythe closing of said switch, comprising a plurality of relays connected rees before and arranged so that the movable elements of the res ectivc relays must simultaneously be in pre etermined positions to enable said switch to be closed, one of said relays being connected to said sources of eleotromo tive force and arranged to tend to move to switch closing position during a predetem "mined range of phase difference between the electromotive forces near phase co-in- 1 cidence and tending to move I away from switch closing position when the phase difference is outside of this range, means for delaying the operation of said relay where= l by it can reach switch closing position during the predetermined range of phase dif-- ference only when the frequencies of said electromotive forces are substantially the,

same, another of said relays being connect: t

ed to said sources of electromotive force and arranged to remain in swltch closing posit-ion during a range of phase difference tion of said connecting means when the electromotive forces of said sources are in synchronism, comprising a control c1rcu1t, a

plurality of contacts arranged in series 1n said control circuit and a" plurality of relays .for controlling 'said .contacts having energizing windings connected in circuit with said sources to rendersaid relays responsive to the phase relation of said electromotive forces, one of said-relays being operative in response to a predetermined phase difl'erence between saidelectromotive forces to close the contacts controlled thereby and upon the occurrence of a smaller predetermined phase difference to open said contacts and another of said relays being operative in response to a redetermined phase difference between sai electromotive forces with a time delay such that the contacts controlled thereby are moved to circuit closing position while said first contacts are in circuit closing POSllJlOIl' only" when the difference between the frequencies of said electromotive forces is below a predetermined value.

3. In a system of the class described wherein two sources of alternating electro motive force are to be synchronized, a switch for connecting the sources together, and means for controlling the closlng of. said switch, comprising a plurality of relays con-- nected and arranged so that the movable elements of the respective relays must simultaneously be in predetermined positions k to enable said switch to be'closed, two of said rela 5 each having windings connected to be individually responsive to a resultant of the instantaneous values of the electromotive forcesto be synchronized, on'eof the windings on eachrelay being arranged to tend to niove the element of the relay oppositely to the tendency of another winding to move the element so thatmovement of the element of each. of said relays depends upon the differential effects of the windings thereon, the windings on each relay being con nected so that. when the electromotive forces are in phase one winding approaches its within a predetermine maximum effect and the other winding its minimum effect, one of said relays being arranged to tend to close while said electromotive forces are within a predetermined :ran e of phase difference, ,means for retar ing the operation of said relay so that I the element thereof can reach circuit closing position only when the fre uencies of the electromotive forces are su stantially the same, the'other relay being constructed to remain closed during a redetermined range of phase difference w ile said electromotive forces are approaching phase coincidence and to move quickly away from switch closing position when the electromotive forces are substantially in phase whereby the switch can be closed only when the frequencies of the electromotive forces are so nearly the same as to permit s chronizing and only during an intervalw ile the electromotive forces are approaching phase co incidence and their base difference is range.

4. in an alternating current electric system. wherein the'electromotive force of an alternating current dynamo electric machine is to'be synchronized with the electromotive force of an alternating current electric circuit, synchronizing'means comprising a plurality of cooperating electroresponsive devices, one. of said devices comprising a movable member, contacts controlled by the movement thereof, and a plurality of motor elements arranged to exert opposing torques on said member, one of said eleinents being connected in circuit to be energized accordance with the vectorial sum of and an- 7 other in accordance with the vectorial difference between saidelectromotive forces, the

construction and arrangement of parts being such that said elements operate to move sai I member to contact closing position upon-the occurrence of a redetermmed haserdifierence between sai electromotive or'ces and to inove said member from contact closing po sition upon the occurrence of a smaller predetermined phase difierence, and another of said devices eomprisin a movable member, contacts controlled y the movement,

thereof, means for retarding the movement of said member, and a plurality of motor elements arranged to exert opposing torques on saidmemben one of said elements being connected in circuit to be energized in accordance with the vectorial sum of and another in accordance'withthe vectorial difference between said electromotive forces whereby movement of said member to contact closing position is eflected in accordance with the phase difference between said electromotive forces, the construction and arrangement of arts be' such that when the difference tween t e frequencies of said electromotive forces exceeds a predetermined amount said member will tend to.

reach contact closing psition subsequently to the movement of said first member from contact closing position 5. In an alternating current electric sys tem wherein two sources of alternating elec tromotive force are to be. synchronized, means for connecting the sources, and means for controlling the closin of said connecting means comprising a p urality of cooperatmg electroresponsive devices, each of said devices comprising a movable member and having energizing windings arranged to exert opposing effects thereon," the energizing windings of each of two of said devices being connected in circuit with said sources to be energized respectively in accordance with the sum of and diiierence between the instantaneous values of the electromotive forces to render the devices operative in response to the phase relation thereof, the movable member of one of said two devices being operative in response to a predetermined phase difference between said elec-' tromotive forces to move to circuit closing position and to move to circuit opening position in response to a smaller predetermined phase difference and the other of said two devices comprising means for retarding the movement of the movable member thereof whereby the member is operative in response to a redetermined phase diiierence'between the e ectromotive forces to move to circuit closing position with a time delay such that when the difierence between the frequencies-v of said electromotive forces exceeds a predetermined amount circuit closing position is reached subsequently to the movement of said first member to circuit opening position, and another of said plurality of-devices having the energizing windings thereof connected in circuit with said sources to be energizedin accordance with the respective values of the electromotive forces thereof whereby the movable member is moved to circuit opening position upon the occurrence of a predetermined difference between the electromotive forces, the construction and arrangement of parts being such that the movable elements of said plurality of electroresponsive devices must simultaneous 1y be in predetermined ositions to enable said connecting means to e closed,

6 In an alternating current electric system wherein two sources ofalternating, electromotive force are to be synchronized, synchronizing means comprising a control circuit and a lurality o cooperating electroresponsive evices for controlling said circuit,'one of said devices comprising a rotatable contact controlling member and a phrra-lity of motor elements arranged to exert opposing torques thereon connected in circuit with said sources to be energized in accordance with the vectorial sum of and difference between the electromotive forces thereof respectively, the construction and arrangement of parts'being such that upon the occurrence of a p edetermined phase diffcrence between the electromotive forces said member is quickly moved to circuit closing position and upon the occurrence of a smaller predetermined phase difference is quickly moved to circuit opening position, another of said devices comprising a rotatable contact controlling member, means for retarding the movement thereof and a plurality of motor elements arranged to exert opposing torques thereon connected in circuit with. said sources to be energized in accordance with the vectorial sum of and difference be tween the electromotive forces thereof respectively, the construction and arrangement of parts being such that upon the occurrence of a predetermined phase difierence between the: electromotive forces said memher is moved to circuit closing position with a time delay such that when the difl'erence between the frequencies of said electromotive forces exceeds a predetermined amount said member will tend to reach circuit closing position subsequently to the movement of said first member to circuit opening position.

7. In an alternating current electric system wherein two sources of alternating electromotive .force are to be synchronized, means adapted to be operated to connect said sources, and means for effecting the operation of said connecting means when the electromotive forces of said sources are substantially equal and in synchronism, comprising a control circuit, a plurality of relatively movable cooperating contacts arranged in series in said control circuit and a plurality of relays for controlling said contacts, two of said relays having energizing windings connected incircuit with said sources to render said relays responsive to the phase relation of the electromotive forces thereof, one of said two relays being operative in response to a predetermined phase ,diiference between the electromotive forces to close the" contacts controlled thereby and hold them closed until the occurrence of a smaller predetermined phase difference between said electromotive forces, and another of said two relays being operative in, response to a predetermined phase difference between said electromotive forces with a time delay such that the contacts controlled thereby are moved to circuit closing position while said first contacts are in circuit closing position only when the difference between the fr noncies of said'electromotive forces is be ow a) predetermined value and another of said lurality of relays having energizing win ings connected in circult with said alternator andsaid circuit respectively to render said relay operative in response to the difference between said eleciromolive forces whereby the contacts controlled thereby are moved to circuit opening position upon the occiirrence of a predetermincd diilerencc between said electromotive forces.

8. In an alternating current electric system' wherein two sources of alternating electromotive force are to be synchronized, means for connecting said sources, means comprising aeontrol circuit for effecting the operation of said connecting means, and means for controlling said control circuit comprising a plurality of electroresponsive devices each including a rotatable member, contacts controlled thereby and arranged in series in said control circuit and a plu 'ality of motor elements constructed and arranged to exert opposing torques on said rotatable member irrespective of the directions of the currents in the energizing windings thereof, and each of said devices having the energizing winding of one of the motor elements connected in circuit to be energized in accordance with the sum of the electrometive forces of said machine and said circuit and the energizing winding of another of said elements connected in circuit to be energized in accordance with the difference between said electromotive forces whereby said devices are responsive to the phase clifference and ditl'erence between the frequencies of said electromotive forces, the rotatable member of one of said devices being adapted upon movementthereof in response to the occurrence of a difference between the torques exerted thereon by said motor elements to increase the effect of the element exerting the greater torque and decrease the eli'cct of the element exerting the smaller torque whereby the predominant motor element is rendered more effective, the constrnction and arrangen'ient of parts being such that said motor elements operate to move said member to contact controlling po'- sition upon the occurrence of a predetermined phase diiferenceand to hold said member in contact closing position until the occurrence of a smaller predetermined phase difference, and another of said devices comprising l'neans for retarding the movement of the rotatable member thereof, the construction and arrangement of parts being such that when the difference between the frequencies of said electromotive forcesis below a predetermined value said rotatable member is caused to move tocontact closing position while the contacts of said first device are closed whereby said control circuit is completed to effect the closing of said connecting means.

I In witness whereof, I have hereunto Set my hand this 28th day of July, 1922.

OLIVER C. TRAVER. 

